Morphophysiological diversity in rice: A trait-based framework for carbon capture, allocation, and genotype selection

Rice (Oryza sativa L.) provides a primary source of caloric intake for over half of the global population. Aligning grain production with climate mitigation requires understanding how plant traits influence carbon balance under contrasting water regimes, which affect both trait expression and the fate of plant-derived carbon in soil and greenhouse-gas emissions. Here, the morphological and physiological attributes that govern carbon acquisition, allocation, and retention in rice were reviewed. Belowground, root traits contribute through soil exploration, rhizosphere activity, and structural accumulation, influencing resource acquisition, carbon inputs, and gas transport. Aboveground, shoot architecture, stay-green behavior, and source–sink coordination regulates canopy photosynthesis, reserve remobilization, and allocation to grain and residues. These complementary functions across genotypes, developmental stages, and water regimes, distinguishing plant carbon gain from soil retention and the net greenhouse-gas balance, were examined. Four operational archetypes, deep explorer, source maximizer, sink maximizer, and balanced integrator, are proposed as combinations of candidate traits for rice improvement and management. These proposed selection criteria are distinct from previously published observations, and their combined performance requires field validation. Evaluation would consider calibrated multimodal phenotyping with field measurements of yield, carbon allocation, ecosystem carbon budgets, and greenhouse-gas balances. The central hypothesis proposed as a result of this review is as follows: Combining deep root exploration with a coordinated supply of assimilates, the remobilization of reserves, and grain demand could improve carbon retention while maintaining grain yield, with outcomes that depend on the water regime and the fate of the residues.